Process for improving the wear resistance of steel shot

ABSTRACT

PRODUCTION OF STEEL SHOT OF IMPROVED WEAR RESISTANCE WHICH IS (A) SUITABLE FOR USE AS A BLASTING AGENT IN SURFACE TREATMENT, (B) FORMED OF PARTICLES CHARACTERIZED BY SOLIDITY, FREEDOM FROM STRAINS, SMOOTHNESS, ROUNDNESS AND FREEDOM FROM SUPERFICIAL CRACKS, AND A PARTICLE SIZE BETWEEN 0.01 AND 3.0 MM., AND (C) CONTAIN BETWEEN 1.1 AND 3.3 WEIGHT PERCENT SILICON, BETWEEN 0.05 AND 0.4 WEIGHT PERCENT CARBON, BETWEEN 0.1 AND 0.8 WEIGHT PERCENT MANGANESE, BETWEEN 0 AND 1.0 WEIGHT PERCENT OF ONE OR MORE CUSTOMARY STEEL-ACCOMPANYING MATERIALS, THE BALANCE BEING IRON. THE IMPROVED STEEL SHOT IS PORDUCED BY HEATING IT FOR A PERIOD OF BETWEEN ABOUT 1 AND 5 HOURS TO TEMPERATURES BETWEEN 200 AND 500*C.

Mar cH 14; "I972 BORN ETAL 3,64 937'0 PROCESS FOR IMPROVING THE WEAR RESISTANCE OF STEEL SHOT Filed July 18, 1969 2 Sheets-Sheet l A Examplej 2.2%51'; 0.2220 [:1 Exampleg 2.34 7511;030Z 6' Z 50 *[ndex Nwrzberoffiassages s g I I I I I I I I I 100 150 200 250 300 350 400 450 .500 Annealing Temperature Z In luence of ameafu'g iemparmfure upon llze wear rasislaiwe -fndax) 0 deal s/wi pmauced according 50 Example! and Examp 2 (I l/weak period Z/wurs) March 14, 1972 w, BORN ETAL 3,649,370

PROCESS FOR IMPROVING THE WEAR RESISTANCE OF STEEL SHOT Filed July 18, 1969 2 Sheets-Sheet 2 A Examplei 22251302220. U Example? 231%51'; 0.3026.

Z w "Index N lumber 0/ Passages I l I I I I I 0.5 1 1.5 2 25 3 3.5 4

Arzlzealmgperzbd ill lzours I rlflzwrwe q" [/10 walbzg' period 1500/1 2%? wear resistance Z -llzdar) 0/ steel .skol produced deco/dig Z0 Example] for all annealing zengaerafwe 0/ 350C. azzdazcardz'rg f0 frm'gole formz amzezrlizg fiszrzpamzwv 0f 300$.

nited States Patent 3,649,370 PROCESS FOR IMPROVING THE WEAR RESISTANCE OF STEEL SHOT Friedrich Wilhelm Dorn, Hurth, near Cologne, Klaus Frank, Hermulheim, near Cologne, Dietrich Gleisberg, Hurth, near Cologne, Joachim Kandler, Lechenich, and Hans Dieter Thiel, Hurth, near Cologne, Germany, assignors to Knapsack Aktiengesellschaft, Knapsack, near Cologne, Germany Filed July 18, 1969, Ser. No. 842,876 Claims priority, application Germany, July 30, 1968, P 17 58 724.5 Int. Cl. B22d 25/02; C21d 1/26 U.S. Cl- 148-3 2 Claims ABSTRACT OF THE DISCLOSURE Production of steel shot of improved wear resistance which is (a) suitable for use as a blasting agent in surface treatment, (b) formed of particles characterized by solidity, freedom from strains, smoothness, roundness and freedom from superficial cracks, and a particle size between 0.01 and 3.0 mm., and (c) contain between 1.1 and 3.3 weight percent silicon, between 0.05 and 0.4 weight percent carbon, between 0.1 and 0.8 weight percent manganese, between 0 and 1.0 weight percent of one or more customary steel-accompanying materials, the balance being iron. The improved steel shot is produced by heating it for a period of between about 1 and 5 hours to temperatures between 200 and 500 C.

German published specification 1,254,366 describes silicon-containing steel alloys formed of shot particles, which are characterized by solidity, freedom from strains, smoothness, roundness and freedom from superficial cracks, contain between 0.05 and 1.7% carbon, between 1.1 and 8% silicon, optionally between 0.1 and 2.0% manganese, between 0 and 5% chromium, between 0 and 5% nickel, between 0 and 5% copper and between 0 and 5% aluminum, the balance being iron, and are used as blasting agents in the treatment of metal, stone or glass surfaces.

The particle wear index Z 50/n=515 is an index of the wear resistance of steel shot which combines good peening and cleaning properties with a good roughening depth. The process of the present invention which describes a novel type of heat treatment (annealing treatment) now enables the wear resistance of the steel shot described in DAS 1,254,366 to be further improved up to a particle wear index Z 50/n=750 to 950 without appreciable impairment of the steel shots further use properties.

The present process for improving the wear resistance of steel shot, which is (a) suitable for use as a blasting agent in the treatment of metal, stone, ceramic or glass surfaces, (b) formed of particles characterized by inner solidity, freedom from strains, smoothness, roundness and freedom from superficial cracks, and a size between 0.01 and 3.0 mm., and (c) contain between 1.1 and 3.3 weight percent silicon, between 0.05 and 0.4 weight percent carbon, between 0.1 and 0.8 weight percent maganese, between 0 and 1.0 weight percent of one or more customary steel-accompanying metals, such as chromium, nickel, copper, titanium, aluminum, molybdenum or tungsten, the balance being iron, comprises more especially heating the steel shot for a period of between about 1 and 5 hours, preferably between about 1.5 and 2.5 hours, to temperatures between 200 and 500 C., preferably between 250 and 400 C.

3,649,370 Patented Mar. 14, 1972 ice The steel shot particles of which the wear resistance shall be improved are produced as usual, preferably however by subjecting a steel melt having a temperature between 1500 and 1800" C. and prepared, for example, by electrothermal means, to atomization or nozzle-spraying using water, steam, air or nitrogen under a pressure of between 1 and 13 atmospheres gauge, or by causing a stream of the steel melt having a temperature of between 1500 and 1800 C. to arrive on a granulating plate, cone or groove, and forthwith quenching the molten particles with an excess of water.

The steel melt can be prepared in an electric furnace, an arc furnace or induction furnace using, for example, scrap and the desirable alloy addends as the starting material. The steel melt should conveniently contain between 1.1 and 3.3% silicon, between 0.05 and 0.4% carbon, between 0.1 and 0.8% manganese, and optionally up to 1% of one or more customary steel-accompanying metals, such as chromium, nickel, copper, titanium, aluminum, molybdenum or tungsten, which may also derive from the scrap. A steel me-lt so composed has a melting point higher than 1493 C. To ensure uniform distribution of all of the components, it is necessary for the melt to be heated to a temperature at least C. higher than its respective melting point.

In the accompanying graphs, FIGS. 1 and 2 illustrate the influence of the annealing temperature and period on the wear resistance of the steel shot produced in Examples 1 and 2 hereinafter.

EXAMPLE 1 A basic-lined arc furnace was used to melt therein 390 kg. scrap iron (0.2% Si; 0.15% C; 0.4% Mn) and kg. return material (2.2% Si; 0.20% C) under a covering slag with a CaO/SiO -ratio larger than 1.5, which were subsequently alloyed with 46 kg. ferrosilicon 45 (44.8% Si). The resulting melt, which had a temperature of 1750 C., was deoxidized using 0.5 kg. aluminum, just prior to atomizing it. The melt was delivered through a pouring gate with an opening 13 mm. wide so as to centrally arrive in a spray nozzle, and disintergrated using steam under a pressure of 1.9 atmospheres gauge. The resulting shot, which was formed of particles with a size between 0 and 3.5 mm., had the following chemical composition:

Percent The shot particles with a size between 0.2 and 3.0 mm. were sieved out and annealed for 2 hours at 350 C. The particles with a size of up to 0.2 mm. (undersize) and those with a size between 3.0 and 3.5 mm. (oversize) were used as a return material (see above) and melted again.

EXAMPLE 2 An acid-lined mains-frequency crucible induction furnace was used to melt therein 1060 kg. scrap iron (0.2% Si; 0.5% Mn; 0.4% C) and 42 kg. ferrosilicon 75 (73.4% Si).

The resulting melt, was overheated to 1630 C., deoxidized using 0.8 kg. aluminum, and atomized with steam under a pressure of 1.9 atmospheres gauge. The resulting shot was composed of The steel shot produced in the manner set forth in Examples 1 and 2 was tested in a blasting agent-testing machine (type KP 1 of Messrs. Georg Fischer, Schaflhausen) The tests were conducted at a velocity of 8000' r.p.m. of the centrifugal blower. This corresponded to a discharge velocity of about 80 m./ second for a diameter of 120 mm. of the centrifugal blower. The testing machine was provided with seven bafile plates and a wear plate. Each of the blasting agents, formed of particles with a size between 1.25 and 1.6 mm. (nominal diameter n of the particles=1.25 mm.), was used in a quantity of 1000 grams. The number of revolutions of the centrifugal blower and the particle size range were kept constant. This enabled the wear resistance and the further properties of the steel shot to be kept free from the influence of these two factors.

TABLE Steel shot, Steel shot, Example 1, Example 2, Sic0n- Chilled annealed annealed taining cast Steel shot;

for 2 hours for 2 hours steel iron at 350 C. at 300 C. shot 1 shot A B Z 50/11 875 840 515 10 640 695 I (mrrL) 0. 65 0. 75 0. 82 1. 02 0. 31 0. 71 A (mg/passage 14. 1 13.0 18. 0 20. 0 10. 7 15.3 R (microns) 120 135 149 90 119 125 1 DAS 1 254 366.

and compared with further shot types having the follow- We claim:

ing composition in weight percent:

As taught in DAS 1,254,366, the data indicated in the following table were determined as an index of the use properties of a blasting agent:

(.1) The particle wear index Z 50/11 is the index of wear resistance. The symbol Z 50/ n represents the number of passages of 1000 grams blasting agent through the testing machine until the weight proportion of particles with a size larger than the nominal diameter 11 of the particles is found to have decreased to a value of 50% of the initial value;

(2) The peening activity or intensity I according to Almen, characterized by the rise in mm. of the center of a small test plate after being peened with 2000 grams blasting agent;

(3) The abrasion A as the cleaning activity-index, determined as loss in weight of a wear plate, based on the passage of 1000 grams blasting agent;

(4) The roughening depth R as the mean surface roughness of the wear plate.

1. A process for improving the wear resistance of steel shot which is (a) suitable for use as a blasting agent in the treatment of metal, stone, ceramic and glass surfaces, (b) formed of particles characterized by inner solidity, freedom from strains, smoothness, roundness and freedom from superficial cracks, and a particle size between 0.01 and 3.0 mm., and (c) contain between 1.1 and 3.3 weight percent silicon, between 0.05 and 0.4 weight percent carbon, between 0.1 and 0.8 weight percent manganese, between 0 and 1.0 weight percent of at least one customary steel-accompanying metals, selected from the group consisting of chromium, nickel, copper, titanium, aluminum, molybdenum and tungsten, the balance being iron, which comprises heating the steel shot for a period of between about 1 and 5 hours to temperatures between 200' and 500 C.

2. The process of claim 1, wherein the steel shot is heated for a period between about 1.5 and 2.5 hours to temperatures between 250 and 400 C.

References Cited UNITED STATES PATENTS 3,245,840 4/1966 Libman 148-3 RICHARD O. DEAN, Primary Examiner U.S. Cl. X-R. 

